The present invention relates to the general subject matter of detecting objects in water and, more particularly, to systems and methods locating fish or subsurface objects using boat-mounted sonar.
The average fisherman or boater today is very familiar with conventional boat-mounted sonar devices of the sort most useful in recreational fishing and boating. These sorts of devices, conventionally referred to as xe2x80x9cfish findersxe2x80x9dor xe2x80x9cdepth sounders,xe2x80x9d have been available for some time and are designed to provide the user with a generalized image of the fish and underwater landscape/features proximate to the vessel. The avid fisherman can use these sorts of devices to locate schools of fish in the water beneath him, thereby increasing the chances that he will not leave empty-handed at the end of the day. Additionally, these devices can provide an estimate of the depth of the water, which is useful both for searching out potential fish habitats and for navigation.
In a typical configuration, the fish finder consists of two components: an underwater transducer and an on-board image display device, i.e., the sonar unit. The image display device might be as simple as a row of LED lights that indicate the distance to the water bottom or as complex as a screen (usually an LCD screen) that offers simultaneous multi-window presentations of system parameters and underwater views.
Conventionally, the image that is presented on the display device is based on the returned signals (echoes) produced in response to sonar transmissions. In a typical arrangement, the sonar originating device is a transducer that is mounted on the boat below the water line. When activated, the transducer radiates high-frequency sound energy into the water beneath the boat where it travels through the water until it encounters a density change, which change might be indicative of, for example, a fish, an underwater obstacle, the water bottom, a water temperature change, etc. When such a change is encountered at least part of the sonic energy that impinges on the target is reflected at the interface and returned toward the source. The returning signal is then detected and then manipulated for subsequent presentation on the display device for use by the fisherman.
The reflected signal is typically sensed as a function of the elapsed time between the origination of the signal and receipt of its returned reflection. Of course, given an approximate velocity of sonic energy in water, it is straightforward and conventional to display the returning signal as a function of xe2x80x9cdepthxe2x80x9d, although in reality that conversion is only strictly appropriate for objects directly below the boat and transducer.
During operation, the transducer generates pulses of sound energy at regular intervals. This energy radiates downward (assuming, of course, that the transducer is oriented to point downward) and outward in a shape that is roughly conical. However, it is inevitable that some of this energy will xe2x80x9cleakxe2x80x9d horizontally. Additionally, the returning reflections are broadly dispersed and may be received away from their point of origination.
The foregoing presents a particular problem when multiple sonar devices are used in close proximity to one another. As a particular example, when two sonar devices are mounted on the same boat it can be difficult for either to operate normally because direct and reflected signals from one unit are received by the other. This causes artifacts in the form of clutter and false bottoms to appear on the display device of the receiving unit. In extreme cases, the two units can interfere with each other to the point of making both essentially useless.
Placing multiple sonar units on a single boat is particularly popular on larger boats (e.g., so that bow and stern views are both available) and on boats that carry multiple fishermen. In the later case, multiple fish finding units allow each boater to control the display parameters of his or her own unit. However, in these situations, such a collection of sonar units is often not practical because of interference from adjacent units.
Others have sought to solve the problem of interference caused by sonar units that are used in close proximity. For example, among the approaches that have been utilized in the past is modifying the transmitting frequencies of each transducer on the boat to make them widely separated from each other. Provided that the frequencies are separated sufficiently, this has the effect of making the signals from one unit largely undetectable by the other transducers. However, if the selected frequencies are so separated this modification changes the character of the transmitted and reflected ultrasonic wave, as different frequencies propagate and are absorbed or reflected differently. This will result in changes in the reflected waveform which may reduce the effectiveness of internal software that automatically looks for a certain reflected waveform when it detects and tracks reflections from the shore, water bottom, etc.
Thus, what is needed is an apparatus and method for allowing multiple fish sensing devices to be used in close proximity with each other without causing interference. The apparatus should allow all of the individual sonar units to operate at the same frequency, if that is desired.
Heretofore, as is well known in the recreation arts, there has been a need for an invention to address and solve the above-described problems. Accordingly, it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a device that would address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.
According to a preferred aspect of the instant invention, there is provided a synchronized sonar apparatus that is suitable for use when multiple fish finding units are used in close proximity with each other. In simplest terms, one preferred embodiment of the instant invention reduces or eliminates interference between adjacent units by causing all of them to activate or xe2x80x9cfirexe2x80x9d at the same time. As a consequence, all of the units will also be xe2x80x9clisteningxe2x80x9d for the returning reflections at the same time. Thus, cross-unit interference is largely eliminated.
In more particular, according to a preferred embodiment of the instant invention there is provided a system which interconnects and synchronizes multiple same-frequency sonic sources so that each may operate without interfering with the others. The sonic sources are electronically synched so that they transmit like signals at the same time, thereby eliminating the interference that is caused by the asynchronous transmission and returning of signals generated by the other sonar devices.
According to another embodiment of the instant invention, there is provided a sonar system where the sonic sources are electronically connected and fired according to a predetermined timing rule, wherein the timing is chosen so that the firing transducers do not interfere with each other. By way of a first example, the transducers could be instructed to fire sequentially, with each transducer xe2x80x9cwaitingxe2x80x9d a period of time at least equal to the two way transducer-to-water bottom travel time of the transducer that fired ahead of it, thereby allowing the signal from the previously-fired transducer to be recorded before a new signal is introduced into the water. Obviously, the time separation between firings could either be a fixed value or a value that is adaptively determined based on local water depths, temperatures, characteristics of the networked transducers, etc. As another example, the transducers could be timed to fire sequentially, but separated in time so that the down-going waves experience constructive interference, i.e., using the multiplicity of transducers to form a tuned array.
The foregoing has outlined in broad terms the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the a drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Additionally, the disclosure that follows is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. Further, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention. Further objects, features, and advantages of the present invention will be apparent upon examining the accompanying drawings and upon reading the following description of the preferred embodiments.